Method and system for monitoring a tire air pressure

ABSTRACT

A method of monitoring a tire pressure, comprises the steps: measuring at least one parameter that influences the tire pressure, calculating the optimum tire pressure ρ opt  on the basis of the at least one measured parameter, comparing a measured tire pressure p with the optimum tire pressure ρ opt  in order to generate a deviation signal in the event of a predetermined deviation.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method and a system for monitoring atire air pressure.

[0002] The air pressure in a tire is typically subjected to specificchanges. These changes in the tire air pressure can be caused, forexample, by various parameters such as the ambient air pressure aroundthe tire. Likewise, the air pressure in a tire changes depending onwhether the tire is used in warmer or colder areas.

[0003] U.S. Pat. No. 5,895,846 discloses a method of processing signalsin a system for monitoring tires on a vehicle during its operation. Inthis case, only the tire pressure and the internal temperature of thetire but no further parameters that determine the air pressure in a tireare taken into account, so that a defect in the tire may mistakenly bedetected.

SUMMARY OF THE INVENTION

[0004] The object of the invention is to provide a method and system formonitoring a tire air pressure, it being possible to determine reliablywhether there is an optimum tire pressure in spite of the effect ofvarious factors which determine the tire air pressure.

[0005] This object is achieved by a method of monitoring a tirepressure, comprising the steps of:

[0006] measuring at least one parameter that influences the tirepressure;

[0007] calculating an optimum tire pressure on the basis of the at leastone measured parameter;

[0008] comparing a measured tire pressure with the optimum tire pressurein order to generate a deviation signal in the event of a predetermineddeviation, the predetermined deviation being defined by an upper andlower limit and, in each case when the deviation signal generatedexceeds the upper limit or falls below the lower limit, a deviationvalue is increased in order to generate an alarm signal when thedeviation value reaches a predetermined threshold value, and thedeviation value is reduced when no deviation signal is present.

[0009] A system for monitoring a tire pressure, comprises at least onetire to be monitored, at least one sensor for measuring at least oneparameter of the at least one tire that influences the air pressure, anair pressure sensor for measuring a current tire air pressure, and anevaluation unit, which receives the at least one parameter measured bythe sensor and measured data from the air pressure sensor. Theevaluation unit calculates an optimum tire pressure on the basis of theat least one measured parameter and compares the measured tire pressurewith the optimum tire pressure in order to generate a deviation signalin the event of a predetermined deviation. The predetermined deviationis defined by an upper and lower limit and, in each case when thedeviation signal generated exceeds the upper limit and falls below thelower limit, a deviation value is increased in order to generate analarm signal when the deviation value reaches a predetermined thresholdvalue, and the deviation value is reduced when no deviation signal ispresent.

[0010] Other advantageous developments of the invention are specified inthe dependent claims.

[0011] According to the method as claimed in claim 1, the influence ofvarious parameters that influence the tire air pressure can be takeninto account reliably during the monitoring of the air pressure in thetire.

[0012] In this case, a tolerance band is defined, within which acurrently measured tire air pressure may deviate from an optimum tireair pressure without an alarm signal being generated.

[0013] According to the method as claimed in claim 2, it is possible toadapt the method to various vehicle types easily, since avehicle-specific tire pressure, for example one specified by the vehiclemanufacturer, is taken into account in monitoring the tire pressure.

[0014] According to claims 3 to 6, various parameters that determine thetire air pressure are taken into account in monitoring an optimum tireair pressure. In this way, the optimum tire air pressure can becalculated at any time, even when external conditions change.

[0015] According to claim 7, the tolerance band can be variable, bywhich means it can be adapted to various parameters that influence thetire air pressure. Thus, by using the method according to the invention,for example secure detection of a tire fault can be carried out,external influences being taken into account.

[0016] According to claims 8 and 9, the driver of a vehicle whichcontains at least one tire whose tire air pressure is to be monitored isinformed, for example, about a pressure drop in the monitored tire. Thisis done, for example, at a gas station, where there is the possibilityfor the driver to refill the tire with air.

[0017] According to claims 10 and 11, the driver is informed about thestill permissible loading of the vehicle. This can be carried outcontinuously or only when a permissible loading limit is exceeded.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention will be described in more detail below using apreferred exemplary embodiment and with reference to the appendeddrawings, in which:

[0019]FIG. 1 shows a block diagram of a preferred exemplary embodimentof a system according to the invention; and

[0020]FIG. 2 shows a flow chart to explain the functioning of the systemaccording to the invention or the method according to the invention.

[0021]FIG. 1 shows a block diagram of a preferred exemplary embodimentof the system according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] As FIG. 1 shows, a pressure sensor 4 for registering the airpressure within the tire is arranged in a vehicle tire 2. Theconstruction and mode of action of such a sensor are known per se andwill therefore not be explained. The pressure sensor 4 does notnecessarily have to be arranged in the interior of the tire; it can alsobe arranged on a valve, so that the pressure-sensitive element of thepressure sensor 4 registers the internal pressure in the tire. Theoutput signal from the pressure sensor 4 is transmitted to an evaluationunit 8 via a radio transmission link 6. However, depending on theconstruction and arrangement of the sensor, this can also be donemechanically via wiping contacts or, as in accordance with the preferredsystem, wire-free in a manner known per se, for example by means of atransponder which communicates with a transmitter/receiver unit 10 whichconditions signals transmitted via the transponder and supplies them toinputs of the evaluation unit 8. Connected to further inputs of theevaluation unit 8 are an ambient air pressure sensor 12, a vehicleloading state sensor 13 and a speed sensor 14.

[0023] The evaluation unit 8 contains, in a manner known per se, amicroprocessor 16 having a program memory 18 and a data memory 20. Oneoutput of the evaluation unit 8 is connected to a warning device 22, forexample a warning lamp or a display in a vehicle switch panel with, ifappropriate, an additional acoustic indicator.

[0024] A functional example of the unit described will be explainedusing the flow chart according to FIG. 2.

[0025] Following the activation of the method in step S1, according tothe preferred exemplary embodiment, a permanently predefinedvehicle-specific air pressure ρ_(nom) is determined. This can be stored,for example, in a memory known per se. Furthermore, in step S2 aparameter K1 is determined which depends on a measured ambient airpressure ρ_(air), _(momentary). This measured ambient air pressure can,for example, be placed in a relationship with a nominal air pressureρ_(air), _(nom) (for example 1024 mbar), so that for the parameter K1 itis true that K1=ρ_(air), _(momentary)−ρ_(air), _(nom).

[0026] Likewise, in step S2, a further parameter K2 is determined whichaccording to the preferred exemplary embodiment, depends on the vehiclespeed. In step S2, a third parameter K3 is also determined, whichdepends on the vehicle loading. Likewise, in step S2 according to thepreferred exemplary embodiment, a fourth parameter K4 is determined,which takes into account a tire inflation pressure read off from anexternal tire inflation instrument during inflation of the tire to bemonitored.

[0027] The abovementioned parameter K4 is used, for example, to takeaccount of the fact that the driver of a vehicle provides the tire fromthe start with an air pressure which, for example, is 0.2 bar above thetire air pressure recommended by the manufacturer.

[0028] Of course, fewer or else more parameters which can influence theoptimum tire air pressure can also be taken into account.

[0029] A current tire air pressure, likewise determined in step S2, isthen compared with, for example, permanently predefined threshold valuesin step S3. If these threshold values are violated, then the driver ofthe vehicle is warned immediately in step S4. These permanentlypredefined threshold values are used to warn the driver in good time inthe event of a sudden tire air pressure drop.

[0030] If, in step S3, the permanently predefined threshold values arenot violated by the tire air pressure currently measured in step S2,then the instantaneous optimum tire air pressure is calculated in stepS5. According to the preferred exemplary embodiment of the invention,this is carried out by using the following formula:

ρ_(opt)=ρ_(nom) +K 1+K 2+K 3+K 4.

[0031] In step S6, a tolerance band is then calculated, the optimum tireair pressure determined in step S5 lying within the tolerance band.According to the preferred exemplary embodiment, the upper and the lowerlimits of the tolerance band are permanently predefined. Alternatively,however, the upper and lower limit of the tolerance band could alsodepend on one or more of the abovementioned parameters that influencethe tire air pressure.

[0032] In step S7, a check is made as to whether the currentlydetermined tire air pressure lies within the tolerance band. If this isso, then in step S8 an internal counter is reduced by a predeterminedvalue. According to the preferred exemplary embodiment of the method,this predetermined value is permanently predefined and always the same.Alternatively, however, it is also possible to reduce the counterappropriately on the basis of the distance of the current tire airpressure from the upper and/or the lower limit of the tolerance band.The method is then continued with step S2.

[0033] If the currently determined tire air pressure does not lie withinthe tolerance band, then the counter is increased in step S9. Accordingto the preferred exemplary embodiment, the value by which the counter isincreased in step S9 is variable. In order to determine the value bywhich the counter is to be increased, the distance Δp of the currenttire air pressure from the tolerance band is determined in step S10. Instep S11, on the basis of the distance Δp calculated in step S10, acounter incremental value ΔL is then calculated, ΔL=f(Δp). In step S12,a corresponding counter increment determined in step 11 is then made.

[0034] The value of the counter reached on the basis of the counterincrement carried out in step S12 is then compared with a fixed orvariable threshold value in accordance with the preferred exemplaryembodiment of the method, see step S13 in FIG. 2. If the predeterminedthreshold value is not reached in step S13, the method according to theinvention is continued with the aforementioned steps at step S2. On theother hand, if the threshold value is reached, the driver is informedappropriately in step S14.

[0035] According to the preferred exemplary embodiment, the driver isnot informed immediately but, in step S15, the information is held backuntil the gas-tank cover is opened or until it is detected that thevehicle tank is being filled. Only then, in step S16, is the informationalready present at step 14 output to the driver, and the driver is, forexample, informed about a pressure drop in a tire.

[0036] Alternatively, it is possible for the driver to be informed abouta pressure drop in a tire when starting the vehicle. It may be possiblefor this information to be called up at any time, for example also viapressure on a knob.

Patent claims
 1. A method of monitoring a tire pressure, comprising thesteps: measuring at least one parameter that influences the tirepressure; calculating an optimum tire pressure on the basis of the atleast one measured parameter; comparing a measured tire pressure withthe optimum tire pressure in order to generate a deviation signal in theevent of a predetermined deviation, the predetermined deviation beingdefined by an upper and lower limit and, in each case when the deviationsignal generated exceeds the upper limit or falls below the lower limit,a deviation value is increased in order to generate an alarm signal whenthe deviation value reaches a predetermined threshold value, and thedeviation value is reduced when no deviation signal is present.
 2. Themethod as claimed in claim 1, wherein the optimum tire pressure includesa vehicle-specific parameter.
 3. The method as claimed in claim 1,wherein the optimum tire pressure depends on a first parameter, whichchanges as a function of the ambient air pressure.
 4. The method asclaimed in claim 1, wherein the optimum tire pressure depending on asecond parameter, which changes as a function of the speed of a vehiclewhich has at least one tire whose tire pressure is to be monitored. 5.The method as claimed in claim 1, wherein the optimum tire pressuredepending on a third parameter, which changes as a function of theloading of a vehicle which has at least one tire whose tire pressure isto be monitored.
 6. The method as claimed in claim 1, wherein theoptimum tire pressure depending on a fourth parameter, which changes asa function of the inflation of the tire.
 7. The method as claimed inclaim 1, wherein the upper and/or lower limit of the predetermineddeviation depends on at least an ambient air pressure, a vehicle speed,a vehicle loading and/or a tire inflation.
 8. The method as claimed inclaim 1, wherein the alarm signal generated will be output only when thegas tank cover of a vehicle is opened.
 9. The method as claimed in claim1, wherein the alarm signal generated being output only when refillingthe vehicle having at least one tire whose tire pressure is to bemonitored is detected.
 10. The method as claimed in claim 1, alsocomprising a step for calculating a still permissible loading of avehicle having at least one tire whose tire pressure is to be monitored,from a predetermined value and the currently measured tire air pressure,and for displaying the still permissible loading of the vehicle.
 11. Themethod as claimed in claim 10, wherein the predetermined value is thecalculated optimum tire pressure.
 12. A system for monitoring a tirepressure, comprising at least one tire to be monitored; at least onesensor for measuring at least one parameter of the at least one tirethat influences the air pressure; an air pressure sensor for measuring acurrent tire air pressure; and an evaluation unit, which receives the atleast one parameter measured by the sensor and measured data from theair pressure sensor and wherein the evaluation unit calculates anoptimum tire pressure on the basis of the at least one measuredparameter and compares the measured tire pressure with the optimum tirepressure in order to generate a deviation signal in the event of apredetermined deviation, wherein the predetermined deviation is definedby an upper and lower limit and, in each case when the deviation signalgenerated exceeds the upper limit and falls below the lower limit, adeviation value is increased in order to generate an alarm signal whenthe deviation value reaches a predetermined threshold value, and thedeviation value is reduced when no deviation signal is present.
 13. Thesystem as claimed in claim 12, wherein the evaluation unit receives atleast one parameter out of a plurality of parameters consisting of avehicle-specific parameter, the ambient air pressure, the speed of avehicle, the loading of a vehicle, the inflation of the tire.
 14. Thesystem as claimed in claim 12, further comprising a sensor for detectingwhen the gas tank cover of a vehicle is opened, wherein the evaluationunit only generates the alarm signal upon detection of said opening.